ASA 127th Meeting M.I.T. 1994 June 6-10

Previously a hybrid boundary element and full wave solution technique was
presented for two-dimensional acoustic propagation in laterally inhomogeneous,
vertically stratified medium [W. Seong and H. Schmidt, J. Acoust. Soc. Am.
Suppl. 1 86, S54 (1989)]. The technique involved dividing the range-dependent
ocean into range-independent sectors with the field within each sector
expressed as a boundary integral over the vertical sector boundaries in terms
of a set of unknown boundary displacements. The approach gave both the forward
propagating field and the backscattered component and was global since it
involved the solution of a matrix relation, the coefficients of which were
obtained from matching boundary conditions along vertical cuts distributed
throughout the entire computational domain. However, for ocean environments
with continuously changing bathymetry, the construction of this matrix in a
global manner presents a severe computational load, especially in the amount of
core memory required. This deficiency motivated the search for a more efficient
formulation of the hybrid scheme. By employing the single-scatter
approximation, where the back-scattered component from the forward vertical
boundary is neglected, a computationally efficient forward marching scheme can
be derived. The algorithm is illustrated using various test cases involving
range-dependent bathymetric features.